Brake caliper with plural cylinders and friction pads

ABSTRACT

A disc brake caliper has two limbs which, in use, straddle an outer periphery of a brake disc to support friction pads on each side of the disc. Each caliper limb supports at least two friction pads arranged side by side in a circumferentially sequential array with the trailing edges of each pad abutting the leading edge of any circumferentially adjacent pad in the array to transmit torque loads from one pad to the adjacent pad.

This invention relates to disc brakes for motor vehicles and inparticular but not exclusively to disc brakes for high performance carsor motor cycles.

In a typical disc brake, a brake caliper straddles the outer peripheralmargin of a brake disc, the caliper having at least one hydrauliccylinder therein for applying friction pads to each side of the disc.The calipers are of two basic types, fixed calipers which have hydrauliccylinders on both sides of the disc, and moving calipers in whichtypically the hydraulic cylinder(s) is on one side of the disc fordirect application of friction pad(s) on that side of the disc, and thefriction pads on the other side of the disc are applied by the reactionmovement of the caliper.

With disc brakes of tile type fitted to high performance vehiclesparticularly racing cars or motor cycles the friction pads are extendedover a relatively long arc to maximise the area of friction material incontact with the disc. When the brakes are applied, the leading edge ofthe pads tends to "grab" onto the disc and in the extreme conditionswhich these brakes operate, the leading edges and areas of the pads wearfaster than the trailing areas.

Also due to the arcuate length of the pads, as the pads heat up duringbraking they tend to buckle due to internal expansion causing heatspotting of the friction material followed by material fade.

One way of compensating for the uneven wear has been to provide aplurality of hydraulic cylinders in the caliper, with the cylinders atthe leading areas of the pad being of a smaller diameter than thecylinders at the trailing areas of the pad so that the leading edge areaof the pad is applied to the disc by a smaller load than the trailingedge areas.

It is an object of the present invention to provide a disc brake caliperwhich mitigates the above problems.

Thus according to the present invention there is provided a disc brakecaliper having two limbs which in use straddle an outer periphery of abrake disc to support friction pads on each side of the disc,characterised in that each caliper limb supports at least two frictionpads arranged side by side in a circumferentially sequential array withthe trailing edge of each pad abutting the leading edge of anycircumferentially adjacent pad in the array to transmit torque loadsfrom one pad to the adjacent pad.

Preferably the adjacent abutting trailing and leading edges of the padshave interlocking portions which prevent circumferentially adjacent padsfrom relative radial movement.

The invention will be described by way of example and with reference tothe accompanying drawings in which:

FIG. 1 is a cross-section through a disc brake calliper according to thepresent invention, taken on the line I--I of FIG. 2, and

FIG. 2 is a section on the II--II of FIG. 1.

With reference to FIG. 1 and FIG. 2 there is illustrated a disc brakecaliper 10 for a racing car and which comprises two limbs 11, 12interconnected by three spaced bridge portions 14A,14B,14C. In use thecaliper straddles the outer periphery of a brake disc 15 (shown indotted outline) with a limb located on each side of the disc. One limb12 is connected in use to the torque reaction member e.g. a stub axle towhich the braking loads are transferred.

The two limbs 11 and 12 each have three hydraulic cylinder assemblies16,17,18, circumferentially spaced across the caliper body (that iscircumferentially with respect to the disc) so that the cylinderassemblies 16, 17, 18 in one limb 11 oppose the cylinder assemblies inthe other limb 12. The cylinders each contain pistons 20 which thrustfriction pads 22A, 22B and 22C against the opposed surfaces of the disc.

In the example shown each pad 22A, 22B, 22C is of a one piece so-calledcarbon/carbon construction (i.e. carbon fibre in a carbon matrix)machined to provide a braking or friction material portion 23A, 23B, 23Cand a larger backing plate portion 24A, 24B, 24C. It will be appreciatedthat each pad may alternatively comprise friction material bonded to aseparate backing plate which will typically be steel.

The pads are supported on the caliper body 11 in a circumferentiallysequential arcuate array with the backing plate portion 24 of the twoend pads 22A and 22C each having a lug 26 thereon with an abutmentsurface 25 for abutment against the calliper body 11, 12 during braking.The center pad 22B is held between the two end pads 22A and 22C by theleading and trailing edges 27L, 27T of its braking plate portioninterlocking with the adjacent leading edge 28 of the adjacent pad 22Aand the trailing edge 29 of the adjacent pad 22C. These edges areinterlocked through serpentine curves, but other interlocking shapescould be used. It will be noted that the radial extent RA,RB,RC of eachpad of the array is substantially the same so that each pad sweepssubstantially the same annular contact area on the disc.

Thus any braking loads are transmitted to the caliper circumferentiallythrough the three pads of each array via the abutting interlocking edges27L,27T,28,29. The middle pads 22B in each array are held againstradially inward movement by the two outer pads 22A and 22C which are inturn secured against radially inward movement by plates 31, and all thepads are held against radially outward movement by the caliper body.

The frictional material areas of the pads 22A to 22C increase from theleading pad 22C to the trailing pad 22A (the terms "leading" and"trailing" refer to the pads when used for braking forward motion of thevehicle, indicated by arrow X in FIG. 2, the "leading" pad being thefirst pad which the disc meets as it rotates). Similarly the hydrauliccylinder diameter also increase from the leading cylinder assembly 18 tothe trailing cylinder assembly 16.

This increase in friction material area and cylinder diameter helps, inaddition to promoting even pad wear, to compensate for the increasedheat built up (and hence loss in braking effect) at the pad/discinterface when moving from the leading to the trailing pad.

Because the pads 22A to 22C in each limb 11 and 12 are formedindividually this provides three pad leading edges and since thetendency is for pad leading edges to "grab" the disc, then the totalbraking capacity of the brake caliper is increased because of theincreased number of pad leading edges. Furthermore since each pad has aleading edge then all three pads tend to wear at the same rate.

Also, with carbon/carbon pads there is a tendency for carbon dust tocollect on the brake disc 15 where its presence between the pads anddisc reduces braking efficiency. Such dust collection on the disc iscleaned off during use of the brake by the leading edges of pads. Theprovision of a number of separate pads in each array each with its ownleading edge improves this cleaning effect. Further, since the longarcuate pad area is now divided over three separate pads instead of asingle pad the tendency to buckling and heat spotting is reduced.

Although the invention has been described above as applied to a six pad,six cylinder type caliper, it can be used for other designs such as afour cylinder, four pad caliper, or a six cylinder four pad caliper, andmay be used on sliding or swinging calipers.

Also, since the "grab effect" is spread between a number of separatepads in each array, the invention could be used with the pads in eacharray of equal friction material area and with each pad operated by acylinder of the same diameter.

We claim:
 1. A disc brake caliper having two limbs which in use straddlean outer periphery of a brake disc to support friction pads on each sideof the disc, each limb including a plurality of hydraulic cylinderassemblies, and supporting at least two friction pads arranged side byside in a circumferentially sequential array with the trailing edge ofeach pad abutting the leading edge of any circumferentially adjacent padin the array to transmit torque loads from one pad to the adjacent pad,and each friction pad having at least one corresponding hydrauliccylinder assembly for pushing the respective friction pad independentlyagainst the disc.
 2. A disc brake caliper as claimed in claim 1 in whicheach caliper limb supports three friction pads arranged in acircumferentially sequential arcuate array.
 3. A disc brake caliper asclaimed in claim 2 in which the friction pads each comprise a frictionmaterial portion and a backing plate portion wherein adjacent trailingand leading edges of the backing plate portions are in abutment, and theadjacent friction material portions are spaced from each other.
 4. Adisc brake caliper as claimed in claim 2 in which the abutting adjacenttrailing edges of the pads have interlocking portions.
 5. A disc brakecaliper as claimed in claim 1 in which each limb of the caliper has aplurality of hydraulic cylinder assemblies (16,17,18) therein, therebeing one cylinder assembly for each friction pad for pushing therespective friction pad against the disc.
 6. A disc brake caliper asclaimed in claim 5 in which the friction pads each comprise a frictionmaterial portion and a backing plate portion wherein adjacent trailingand leading edges of the backing plate portions are in abutment, and theadjacent friction material portions are spaced from each other.
 7. Adisc brake caliper as claimed in claim 5 in which the abutting adjacenttrailing edges of the pads have interlocking portions.
 8. A disc brakecaliper as claimed in claim 1 wherein the disc contact areas of thefriction material portions of the pads and the cross section areas ofthe hydraulic cylinder assemblies increase from the leading pads to thetrailing pads.
 9. A disc brake caliper as claimed in claim 8 in whichthe friction pads each comprise a friction material portion and abacking plate portion wherein adjacent trailing and leading edges of thebacking plate portions are in abutment, and the adjacent frictionmaterial portions are spaced from each other.
 10. A disc brake caliperas claimed in claim 8 in which the abutting adjacent trailing edges ofthe pads have interlocking portions.
 11. A disc brake caliper as claimedin claim 1 in which the friction pads each comprise a friction materialportion and a backing plate portion (24A,24B,24C), wherein adjacenttrailing and leading edges of the backing plate portions are inabutment, and the adjacent friction material portions are spaced fromeach other.
 12. A disc brake caliper as claimed in claim 11 in which theabutting adjacent trailing edges of the pads have interlocking portions.13. A disc brake caliper as claimed in claim 1 in which the abuttingadjacent trailing edges of the pads have interlocking portions.
 14. Adisc brake caliper as claimed in claim 13 in which the interlockingportions are of a serpentine form.
 15. A disc brake caliper having twolimbs which in use straddle an outer periphery of a rotatable brake discto support friction pads for contact with each side of the disc, eachlimb including a plurality of hydraulic cylinder assemblies, andsupporting at least two friction pads arranged side by side in acircumferentially sequential array with the trailing edge of each padabutting the leading edge of any circumferentially adjacent pad in thearray to transmit torque loads from one pad to the adjacent pad, and theareas of the pads which contact the disc and the cross section areas ofthe hydraulic cylinder assemblies increasing from a leading pad to atrailing pad considering the pads relative to an intended forwarddirection of rotation of the disc.
 16. A disc brake caliper having twolimbs which, in use, straddle an outer periphery of a brake disc tosupport friction pads on each side of the disc, each limb including aplurality of cylinder assemblies to exert axial pressure against thepads, each limb of said caliper supporting at least two friction padsarranged side by side in a circumferentially sequential array with thetrailing edge of each pad abutting the leading edge of anycircumferentially adjacent pad in th array to transmit torque loads fromone pad to the adjacent pad, and the abutting adjacent trailing andleading edges of the pads have interlocking portions to prevent relativeradial movement between abutting pads and between the pads and the brakecaliper but permitting relative independent axial movement of each padwith respect to any adjacent pad due to pressure independently exertedon each pad by at least one of the hydraulic cylinder assemblies.